Cheap test gauges HIV drug success

Spots of dried blood could help to monitor the success of HIV drugs in the developing world.

Antiretroviral drugs stop the Aids virus from killing key immune cells in the blood. But patients in Africa, for example, often miss out on essential blood-cell monitoring because it requires fresh, refrigerated blood and expensive analytical machines.

But now there is an alternative. "You just need a finger prick," says Alimuddin Zumla of University College London. In a trial on 42 Zambian patients reported in last week's Lancet, Zumla's team has shown that cell counts obtained using dried blood spots are largely comparable to those from hi-tech monitoring.

In western clinics, doctors probe fresh blood samples by mixing them with fluorescent antibodies that latch on to critical immune cells called CD4+ lymphocytes. The fluorescent cells are sorted and counted in a machine. The procedure costs up to $40 a go. In Zumla's test, blood spots on filter paper are allowed to dry, then ferried to a central clinic without refrigeration. This is vital in developing countries, where many rural patients live far from urban clinics.

Technicians analyse the blood spots using a simple, commercially available test involving antibodies that latch on to the CD4+ lymphocytes. The bound antibodies cause a colour change in a solution made from the dried blood: a deeper colour equals a higher cell count.

Zumla says that he has adapted the prototype so that it can also gauge levels of the Aids virus, another key indicator of treatment success. It costs about $1 per test, he says. Cheaper reagents could slash it to only 20 cents. The team hopes to perfect the test with HIV clinics in several African countries. They are also looking for a company to develop it.